The present invention relates to a device and a method for detecting and analyzing deposits.
Industrial plants, like power plants, steel mills, pulp or paper making plants, usually comprise means for conducting or storing fluids, e.g. pipe lines or fluid containers. It is a known issue that organic and inorganic matter deposits on the inner walls of these means for conducting or storing fluids, whereby an accumulation of fouling or scaling deposits at least partially blocks the flow through the conducting means and conducted or stored fluids may become contaminated. This is an unwanted occurrence that causes a number of operational problems such as plugging of equipment, inefficient usage of chemicals, increased utility costs, lost production due to downtime, corrosion, and downgraded products from increased dirt counts.
In principle, one can distinguish between fouling deposits on the one hand and scaling deposits on the other hand. Fouling deposits are organic deposits which often occur in the form of biofilms in aqueous systems. Such biofilms substantially consist of micro-organisms, e.g. bacteria, algae, fungi and protozoa. Contrary thereto, scale depositions occur from inorganic matter that have been identified include e.g. complexes of calcium (carbonate, oxalate, sulfate, silicates), aluminum (silicates, hydroxides, phosphates), barium sulfate, radioactive radium sulfate, and silicates of magnesium.
In order to avoid the accumulation of fouling deposits and in particular the growth of biofilms, biocides are added into the fluid concerned as countermeasures. Scaling deposits can be removed by adding chemical deposit control agents based on homopolymers, copolymers and terpolymers of acrylic acid, methacrylic acid, maleic acid and aspartic acid. Furthermore the chemical deposit control agents can be based on organic phosphonates and their derivatives, as well as on polyphosphates.
The dosage of these biocides and chemical deposit control agents has to be accomplished very carefully and conservative because they are very expensive and pose a health hazard. It is thus necessary to distinguish between scaling and fouling deposits and to determine the thickness of the scaling or fouling deposits.
A method and a device for high precision measurement of a characteristic of a fouling or scaling deposit inside a fluid vessel is disclosed in the prior art document WO 2009 /141 135 A1. An ultrasonic emission signal is emitted by an ultrasonic transducer towards a reflecting area inside the fluid vessel and a distance between the ultrasonic transducer and the reflecting area or between the ultrasonic transducer and a deposit onto the reflecting area is measured by means of evaluating the time-domain reflective signal of the reflecting area or of the deposit covering the reflecting area. The measured distance is compared to a reference distance which has been measured in an initial calibration measurement step without any deposits onto the reflecting area. The difference between the measured distance and the reference distance is a measure for the thickness of the deposition. A disadvantage of this method is that the real distance between the ultrasonic transducer and the reflective area changes e.g. with the temperature or the pressure inside the fluid vessel. Therefore, the current distance between the ultrasonic transducer and the reflective area at the time of measurement cannot accurately defined by a previously measured reference distance. Consequently, the measurement of the thickness of the deposits comprises an unknown offset depending on operational conditions, like pressure and temperature.
Industrial plants usually comprise multiple functional units, like boiler, heat exchanger, condenser, mixer, for instance. These multiple functional units are connected to each other, in particular in series and/or in parallel, via connection pipes and the like.
A problem of known devices for measuring fouling or scaling deposits in an industrial plant is that it is difficult to install suchlike measuring devices inside of the functional units because of e.g. limited installation space or excessively elevated temperatures inside the functional units. Consequently, the devices are provided usually at or in the connecting pipes between the functional units, even though the temperatures inside of the functional units are regularly higher than in the connecting pipes, in particular when the functional unit comprises e.g. a boiler. This is disadvantageous for the quality of the measurements because higher temperatures increase the growth of fouling, so that there is frequently a higher accumulation of deposits inside the functional units than inside of the connection pipes. Consequently, the results measured in the connecting tubes are falsified and the thickness of deposits in the relevant areas cannot be accurately determined.